<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<h1>我的第一段 JavaScript</h1>

<p id="demo">JavaScript 可以更改 HTML 元素的样式。</p>

<script>
  function myFunction(){
    document.getElementById("demo").style.fontSize = "25px";
    document.getElementById("demo").style.color = "red";
    document.getElementById("demo").style.backgroundColor = "yellow";
  }
</script>

<button type="button" onclick="myFunction()">点击我！</button>

</body>
</html>